High performance ballistic composites and method of making

ABSTRACT

Fabrication of ballistic resistant fibrous composites having improved ballistic resistance properties and retained or improved ballistic penetration resistance properties. The composites are formed from high tenacity fibers having a tenacity of at least about 33 g/denier at ambient room temperature after being modified by a plasma treatment or by a corona treatment, without tenacity loss due to said treatments.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 61/531,302, filed on Sep. 6, 2011, the disclosure of which isincorporated by reference herein in its entirety. This application alsoclaims the benefit of U.S. Provisional Application Ser. No. 61/566,295,filed on Dec. 2, 2011, the disclosure of which is incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

The invention pertains to high tenacity fibers having a tenacity of atleast about 33 g/denier at ambient room temperature after being modifiedby a plasma treatment or by a corona treatment, which typically damagesfibers and reduces their tenacity. The invention also pertains tofibrous composites formed from such modified, high tenacity fibers whichhave both a low composite backface signature and excellent V₅₀performance.

DESCRIPTION OF THE RELATED ART

Ballistic resistant articles fabricated from composites comprising hightenacity synthetic fibers are well known. Articles such as bulletresistant vests, helmets, vehicle panels and structural members ofmilitary equipment are typically made from woven, knitted or non-wovenfabrics comprising high tenacity fibers such as SPECTRA® polyethylenefibers or KEVLAR® aramid fibers. For example, U.S. Pat. Nos. 4,403,012,4,457,985, 4,613,535, 4,623,574, 4,650,710, 4,737,402, 4,748,064,5,552,208, 5,587,230, 6,642,159, 6,841,492, 6,846,758, all of which areincorporated herein by reference, describe ballistic resistantcomposites which formed from high tenacity fibers, such as extendedchain ultra-high molecular weight polyethylene (“UHMW PE”) fibers. Eachtype of high tenacity fiber has its own unique characteristics andproperties, and ballistic resistant composites fabricated from hightenacity fibers exhibit varying degrees of projectile penetrationresistance and backface signature (“BFS”).

In many applications, fibers may be encapsulated or embedded in apolymeric matrix material. This is particularly common in thefabrication of non-woven fabrics. In this regard, a definingcharacteristic of a fiber is the ability of the fiber to bond with oradhere with surface coatings, including resin coatings. Strong adhesionof polymeric binder materials is important in the manufacture ofballistic resistant fabrics. Poor adhesion of polymeric binder materialson the fiber surfaces may reduce fiber-fiber bond strength andfiber-binder bond strength and thereby cause united fibers to disengagefrom each other and/or cause the binder to delaminate from the fibersurfaces. This reduces the ballistic resistance properties, also knownas anti-ballistic performance, of such composites and can result incatastrophic product failure. For example, as described in applicationSer. Nos. 61/531,233; 61/531,255; 61/531,268; 61/531,302; and61/531,323, there is a direct correlation between backface signature andthe tendency of the component fibers of a ballistic resistant compositeto delaminate from each other and/or delaminate from fiber surfacecoatings as a result of a projectile impact. By improving the bondbetween a fiber surface and a fiber surface coating, the fiber-fiberdisengagement and/or fiber-coating delamination effect are reduced,thereby increasing friction on the fibers and increasing projectileengagement with the fibers. This improvement in bond strength results inthe improvement of composite structural properties, allowing the energyof a projectile impact to be dissipated in a manner that reduces thebackface deformation of the composite.

As is known in the art, the ability of a fiber to bond with or adherewith surface coatings may be improved by corona treating or plasmatreating the fibers. Corona treatment is a process in which a fiber ispassed through a corona discharge station, thereby passing the fiber webthrough a series of high voltage electric discharges, which tend to acton the surface of the fiber web in a variety of ways, including pitting,roughing and introducing polar functional groups by way of partiallyoxidizing the surface of the fiber. A plasma treatment is similar to acorona treatment but differs from a corona treatment mainly in that aplasma treatment is conducted in a controlled, reactive atmosphere ofgases, whereas in corona treatment the reactive atmosphere is air.

These treatments modify the fibers, such as by ablating the fibersurface, pitting or roughening of the fiber surface, removingcontaminants from the fiber surface, oxidizing the fiber surface,polarizing the fiber surface, causing chain scission and molecularweight reduction of the polymer molecules at the fiber surface, and/orby crosslinking polymer chains near the fiber surface through freeradical bonding. As a result of these modifications, the ability ofsubsequently applied materials to adsorb to, adhere to or bond to thefiber surface is enhanced, thereby reducing the tendency of fibersurface coatings to delaminate, and thereby reducing composite backfacedeformation upon projectile impact. However, it has now been recognizedthat the harsh conditions of plasma treating and corona treating aredestructive of fiber tenacity. Data has shown that fiber tenacitypre-treatment is significantly greater than fiber tenacitypost-treatment. This is undesirable because fiber penetration resistanceis directly proportional to the physical strength of the fibers formingthe composite, so a reduction in physical strength correlates with adecrease in V₅₀ velocity, and achieving the desired improvements in BFScomes with a sacrifice of penetration resistance. Accordingly, there isan ongoing need in the art for a method to produce ballistic resistantcomposites having reduced backface signature without sacrificingsuperior V₅₀ ballistic performance properties. The invention provides asolution to this need.

SUMMARY OF THE INVENTION

The invention provides a modified, high tenacity fiber which has beenmodified by a plasma treatment or modified by a corona treatment, saidmodified, high tenacity fiber having a tenacity of at least about 33g/denier at ambient room temperature.

The invention also provides a modified, high tenacity fiber which hasbeen modified by a plasma treatment or modified by a corona treatment,said modified, high tenacity fiber having a tenacity of at least about33 g/denier at ambient room temperature, said fiber being produced by aprocess comprising the steps of:

a) providing a high tenacity fiber having a tenacity of at least about33 g/denier at ambient room temperature, wherein said fiber has fibersurfaces and wherein said surfaces are at least partially covered by afiber surface finish or wherein said fiber is substantially free of afiber surface finish;

b) where said fiber surfaces are at least partially covered by a fibersurface finish, removing at least a portion of the fiber surface finishfrom the fiber surfaces; and

c) subjecting the high tenacity fiber to a plasma treatment or to acorona treatment under conditions effective to modify the high tenacityfiber;

thereby producing a modified, high tenacity fiber which has beenmodified by a plasma treatment or modified by a corona treatment, whichmodified high tenacity fiber has a tenacity of at least about 33g/denier at ambient room temperature.

Further provided are fiber plies, fabrics, fibrous composites andarticles formed from such fibers.

DETAILED DESCRIPTION OF THE INVENTION

The fibrous composites of the invention are distinguished from otherfibrous composites by having both reduced backface deformation againsthigh velocity projectiles in addition to superior ballistic penetrationresistance. For the purposes of the invention, articles that havesuperior ballistic penetration resistance describe those which exhibitexcellent properties against deformable projectiles, such as bullets,and against penetration of fragments, such as shrapnel. Backfacesignature is a measure of the depth of deflection of either soft or hardarmor into a backing material or into a user body due to a projectileimpact. More specifically, BFS, also known in the art as “backfacedeformation”, “trauma signature” or “blunt force trauma”, is a measureof how much impact a projectile leaves under the armor once the armorstops the projectile from penetrating, indicating the potential blunttrauma experienced by the body underneath the armor. The standard methodfor measuring BFS of soft armor is outlined by NIJ Standard 0101.04,Type IIIA, which identifies a method of transferring the physicaldeformation of a composite resulting from a non-penetrating projectileimpact into a deformable clay backing material held in an open face,box-like fixture. Per the NIJ standard, the armor being tested issecured directly to a front surface of the clay backing and anydeformation of the clay resulting from standardized projectile firingconditions is identified and measured. Other methods may be used tomeasure BFS. The NIJ standard is conventionally used at the present timeto evaluate soft armor composites intended for military use.

A “fiber layer” as used herein may comprise a single-ply ofunidirectionally oriented fibers, a plurality of non-consolidated pliesof unidirectionally oriented fibers, a plurality of consolidated pliesof unidirectionally oriented fibers, a woven fabric, a plurality ofconsolidated woven fabrics, or any other fabric structure that has beenformed from a plurality of fibers, including felts, mats and otherstructures, such as those comprising randomly oriented fibers. A “layer”describes a generally planar arrangement. Each fiber layer will haveboth an outer top surface and an outer bottom surface. A “single-ply” ofunidirectionally oriented fibers comprises an arrangement ofnon-overlapping fibers that are aligned in a unidirectional,substantially parallel array. This type of fiber arrangement is alsoknown in the art as a “unitape”, “unidirectional tape”, “UD” or “UDT.”As used herein, an “array” describes an orderly arrangement of fibers oryarns, which is exclusive of woven fabrics, and a “parallel array”describes an orderly parallel arrangement of fibers or yarns. The term“oriented” as used in the context of “oriented fibers” refers to thealignment of the fibers as opposed to stretching of the fibers. The term“fabric” describes structures that may include one or more fiber plies,with or without molding or consolidation of the plies. For example, awoven fabric or felt may comprise a single fiber ply. A non-woven fabricformed from unidirectional fibers typically comprises a plurality offiber plies stacked on each other and consolidated. When used herein, a“single-layer” structure refers to any monolithic fibrous structurecomposed of one or more individual plies or individual layers that havebeen merged, i.e. consolidated by low pressure lamination or by highpressure molding, into a single unitary structure together with apolymeric binder material. By “consolidating” it is meant that thepolymeric binder material together with each fiber ply is combined intoa single unitary layer. Consolidation can occur via drying, cooling,heating, pressure or a combination thereof. Heat and/or pressure may notbe necessary, as the fibers or fabric layers may just be glued together,as is the case in a wet lamination process. The term “composite” refersto combinations of fibers with at least one polymeric binder material. A“complex composite” as used herein refers to a consolidated combinationof a plurality of fiber layers. As described herein, “non-woven” fabricsinclude all fabric structures that are not formed by weaving. Forexample, non-woven fabrics may comprise a plurality of unitapes that areat least partially coated with a polymeric binder material,stacked/overlapped and consolidated into a single-layer, monolithicelement, as well as a felt or mat comprising non-parallel, randomlyoriented fibers that are preferably coated with a polymeric bindercomposition.

For the purposes of the present invention, a “fiber” is an elongate bodythe length dimension of which is much greater than the transversedimensions of width and thickness. The cross-sections of fibers for usein this invention may vary widely, and they may be circular, flat oroblong in cross-section. Thus the term “fiber” includes filaments,ribbons, strips and the like having regular or irregular cross-section,but it is preferred that the fibers have a substantially circularcross-section. As used herein, the term “yarn” is defined as a singlestrand consisting of multiple fibers. A single fiber may be formed fromjust one filament or from multiple filaments. A fiber formed from justone filament is referred to herein as either a “single-filament” fiberor a “monofilament” fiber, and a fiber formed from a plurality offilaments is referred to herein as a “multifilament” fiber.

The reduction in backface deformation results from modifying thecomponent fibers of the fibrous composites to enhance fiber-fiberengagement and/or reduce fiber-coating delamination tendency. Thereduction in fiber-fiber disengagement and/or fiber-coating delaminationupon projectile impact is optimized by plasma treating or coronatreating the fibers after at least partially removing a pre-existingfiber surface finish from the fibers prior to processing the fibers intoa fabric, wherein forming a fabric includes interconnecting the fibersto thereby form woven fabric layers, non-woven fabric layers or anon-woven fiber plies. The removal of fiber surface finishes prior tothe formation of non-woven fabric layers or non-woven fiber plies, orprior to the weaving of woven fabrics, has not hereinbefore been knownbecause the fiber surface finish is generally known as a necessaryprocessing aid as described above. In the fabrication of non-wovenfabrics, a fiber surface finish is generally required to reduce staticbuild-up, prevent fiber tangling, lubricate the fiber to allow it toslide over loom components, and improve fiber cohesion duringprocessing, including during fiber drawing steps. Plasma treating orcorona treating the fibers after removing at least a portion of apre-existing fiber surface finish from the fibers allows the exposedfiber surfaces to be treated directly, thereby modifying the fibersurfaces rather than conducting the treatments on the fiber finish. Thereduction in fiber-fiber disengagement and/or fiber-coating delaminationyields composites having correspondingly superior backface signatureperformance against high velocity projectiles.

While fiber surface finishes are typically needed during conventionalfabric processing, they generally do not contribute to the final fabricproperties. To the contrary, by covering fiber surfaces, the finishinterferes with the ability of the fiber surfaces to contact each other,and interferes with the ability of the fiber surfaces to directly adsorbsubsequently applied adsorbates, such as liquid or solid resins orpolymeric binder materials that are applied onto the fibers, positioningthe adsorbates on top of the finish rather than directly on the fibersurfaces. This is problematic. In the former situation, the finish actsas a lubricant on the fiber surfaces and thus reduces friction betweenadjacent fibers. In the latter situation, the finish preventssubsequently applied materials from bonding directly and strongly to thefiber surfaces, potentially preventing coatings from bonding to fibersaltogether, as well as risking delamination during a ballistic impact.To enhance fiber-fiber friction and to permit direct bonding of resinsor polymeric binder materials to the fiber surfaces, thereby increasingthe fiber-coating bond strength, it is necessary that the existing fibersurface finish be at least partially removed, and preferablysubstantially completely removed from all or some of the fiber surfacesof some or all of the component fibers forming a fibrous composite.

The at least partial removal of the fiber surface finish will preferablybegin once all fiber drawing/stretching steps have been completed. Thestep of washing the fibers or otherwise removing the fiber finish willremove enough of the fiber finish so that at least some of theunderlying fiber surface is exposed, although different removalconditions should be expected to remove different amounts of the finish.For example, factors such as the composition of the washing agent (e.g.water), mechanical attributes of the washing technique (e.g. the forceof the water contacting the fiber; agitation of a washing bath, etc.),will affect the amount of finish that is removed. For the purposesherein, minimal processing to achieve minimal removal of the fiberfinish will generally expose at least 10% of the fiber surface area.Preferably, the fiber surface finish is removed such that the fibers arepredominantly free of a fiber surface finish. As used herein, fibersthat are “predominantly free” of a fiber surface finish are fibers whichhave had at least 50% by weight of their finish removed, more preferablyat least about 75% by weight of their finish removed. It is even morepreferred that the fibers are substantially free of a fiber surfacefinish. Fibers that are “substantially free” of a fiber finish arefibers which have had at least about 90% by weight of their finishremoved, and most preferably at least about 95% by weight of theirfinish removed, thereby exposing at least about 90% or at least about95% of the fiber surface area that was previously covered by the fibersurface finish. Most preferably, any residual finish will be present inan amount of less than or equal to about 0.5% by weight based on theweight of the fiber plus the weight of the finish, preferably less thanor equal to about 0.4% by weight, more preferably less than or equal toabout 0.3% by weight, more preferably less than or equal to about 0.2%by weight and most preferably less than or equal to about 0.1% by weightbased on the weight of the fiber plus the weight of the finish.

Depending on the surface tension of the fiber finish composition, afinish may exhibit a tendency to distribute itself over the fibersurface, even if a substantial amount of the finish is removed. Thus, afiber that is predominantly free of a fiber surface finish may stillhave a portion of its surface area covered by a very thin coating of thefiber finish. However, this remaining fiber finish will typically existas residual patches of finish rather than a continuous coating.Accordingly, a fiber having surfaces that are predominantly free of afiber surface finish preferably has its surface at least partiallyexposed and not covered by a fiber finish, where preferably less than50% of the fiber surface area is covered by a fiber surface finish. Thefibrous composites of the invention comprising fiber surfaces that arepredominantly free of a fiber finish are then coated with a polymericbinder material. Where removal of the fiber finish has resulted in lessthan 50% of the fiber surface area being covered by a fiber surfacefinish, the polymeric binder material will thereby be in direct contactwith greater than 50% of the fiber surface area.

Most preferably, the fiber surface finish is substantially completelyremoved from the fibers and the fiber surfaces are substantiallycompletely exposed. In this regard, a substantially complete removal ofthe fiber surface finish is the removal of at least about 95%, morepreferably at least about 97.5% and most preferably at least about 99.0%removal of the fiber surface finish, and whereby the fiber surface is atleast about 95% exposed, more preferably at least about 97.5% exposedand most preferably at least about 99.0% exposed. Ideally, 100% of thefiber surface finish is removed, thereby exposing 100% of the fibersurface area. Following removal of the fiber surface finish, it is alsopreferred that the fibers are cleared of any removed finish particlesprior to application of a polymeric binder material, resin or otheradsorbate onto the exposed fiber surfaces. As processing of the fibersto achieve minimal removal of the fiber finish will generally expose atleast about 10% of the fiber surface area, a comparable composite whichhas not been similarly washed or treated to remove at least a portion ofthe fiber finish will have less than 10% of the fiber surface areaexposed, with zero percent surface exposure or substantially no fibersurface exposure.

Increasing fiber-coating bond strength also reduces the amount of binderneeded to adequately bind the fibers together. This reduction in binderquantity allows a greater number of fibers to be included in a fabric,which allows for potentially producing lighter ballistic materialshaving improved strength. This also leads to improved stab resistance ofthe resulting fabric composites.

Any conventionally known method for removing fiber surface finishes isuseful within the context of the present invention, including bothmechanical and chemical techniques means. The necessary method isgenerally dependent on the composition of the finish. For example, inthe preferred embodiment of the invention, the fibers are coated with afinish that is capable of being washed off with only water. Typically, afiber finish will comprise a combination of one or more lubricants, oneor more non-ionic emulsifiers (surfactants), one or more anti-staticagents, one or more wetting and cohesive agents, and one or moreantimicrobial compounds. The finish formulations preferred herein can bewashed off with only water. Mechanical means may also be employedtogether with a chemical agent to improve the efficiency of the chemicalremoval. For example, the efficiency of finish removal using de-ionizedwater may be enhanced by manipulating the force, direction velocity,etc. of the water application process.

Most preferably, the fibers are washed and/or rinsed with water as afiber web, preferably using de-ionized water, with optional drying ofthe fibers after washing, without using any other chemicals. In otherembodiments where the finish is not water soluble, the finish may beremoved or washed off with, for example, an abrasive cleaner, chemicalcleaner or enzyme cleaner. For example, U.S. Pat. Nos. 5,573,850 and5,601,775, which are incorporated herein by reference, teach passingyarns through a bath containing a non-ionic surfactant (HOSTAPUR® CX,commercially available from Clariant Corporation of Charlotte, N.C.),trisodium phosphate and sodium hydroxide, followed by rinsing thefibers. Other useful chemical agents non-exclusively include alcohols,such as methanol, ethanol and 2-propanol; aliphatic and aromatichydrocarbons such as cyclohexane and toluene; chlorinated solvents suchas di-chloromethane and tri-chloromethane. Washing the fibers will alsoremove any other surface contaminants, allowing for more intimatecontact between the fiber and resin or other coating material.

The preferred means used to clean the fibers with water is not intendedto be limiting except for the ability to substantially remove the fibersurface finish from the fibers. In a preferred method, removal of thefinish is accomplished by a process that comprises passing a fiber webthrough pressurized water nozzles to wash (or rinse) and/or physicallyremove the finish from the fibers. The fibers may optionally bepre-soaked in a water bath before passing the fibers through saidpressurized water nozzles, and/or soaked after passing the fibersthrough the pressurized water nozzles, and may also optionally be rinsedafter any of said optional soaking steps by passing the fibers throughadditional pressurized water nozzles. The washed/soaked/rinsed fibersare preferably also dried after washing/soaking/rinsing is completed.The equipment and means used for washing the fibers is not intended tobe limiting, except that it must be capable of washing individualmultifilament fibers/multifilament yarns rather than fabrics, i.e.before they are woven or formed into non-woven fiber layers or plies.

The removal of the fiber surface finish prior to fabric formation isespecially intended herein for the production of non-woven fabrics thatare formed by consolidating a plurality of fiber plies that comprise aplurality of unidirectionally aligned fibers. In a typical process forforming non-woven unidirectionally aligned fiber plies, fiber bundlesare supplied from a creel and led through guides and one or morespreader bars into a collimating comb, followed by coating the fiberswith a polymeric binder material. Alternately the fibers can be coatedbefore encountering the spreader bars, or they may be coated between twosets of spreader bars, one before and one after the coating section. Atypical fiber bundle (e.g. a yarn) will have from about 30 to about 2000individual filaments, each fiber typically including, but not limitedto, from about 120 to about 240 individual filaments. The spreader barsand collimating comb disperse and spread out the bundled fibers,reorganizing them side-by-side in a coplanar fashion. Ideal fiberspreading results in the individual fibers, or even individualfilaments, being positioned next to one another in a single fiber plane,forming a substantially unidirectional, parallel array of fibers with aminimal amount of fibers overlapping each other. Removing the fibersurface finish before or during this spreading step may enhance andaccelerate the spreading of the fibers into such a parallel array due tothe physical interaction of the cleaning agent (e.g. water) with whichthe fibers/filaments interact. Following fiber spreading andcollimating, the fibers of such a parallel array will typically containfrom about 3 to 16 fiber ends per inch (1.2 to 6.3 ends per cm),depending on the fiber thickness. Accordingly, removal of the fibersurface finish achieves a dual benefit of enhancing fiber spreading andimproves the bond strength of subsequently applied materials/adsorbateson the fiber surfaces.

After the fiber surface finish is removed to the desired degree, thefibers are subjected to either a plasma treatment or a corona treatment.Both the plasma treatment and the corona treatment will modify thefibers at the fiber surfaces, thereby further enhancing theadsorbability/bonding of a subsequently applied adsorbate (e.g.polymer/resin) on the fiber surfaces. Removal of the fiber finish allowsthese additional processes to act directly on the surface of the fiberand not on the fiber surface finish or on surface contaminants. Plasmatreatment and corona treatment are each desirable for optimizing theinteraction between the bulk fiber and fiber surface coatings to improvethe anchorage of the coatings to fiber surfaces. This modifiedinteraction can easily be seen in improvements in BFS.

Corona treatment is a process in which a fiber is passed through acorona discharge station, thereby passing the fiber web through a seriesof high voltage electric discharges, which tend to act on the surface ofthe fiber web in a variety of ways, including pitting, roughing andintroducing polar functional groups by way of partially oxidizing thesurface of the fiber. Corona treatment typically oxidizes the fibersurface and/or adds polarity to the fiber surface. Corona treatment alsoacts by burning small pits or holes into the surface of the fiber. Whenthe fibers are oxidizable, the extent of oxidation is dependent onfactors such as power, voltage and frequency of the corona treatment.Residence time within the corona discharge field is also a factor, andthis can be manipulated by corona treater design or by the line speed ofthe process. Suitable corona treatment units are available, for example,from Enercon Industries Corp., Menomonee Falls, Wis., from ShermanTreaters Ltd, Thame, Oxon., UK, or from Softal Corona & Plasma GmbH & Coof Hamburg, Germany.

In a preferred embodiment, the fibers are subjected to a coronatreatment of from about 2 Watts/ft²/min to about 100 Watts/ft²/min, morepreferably from about 5 Watts/ft²/min to about 50 Watts/ft²/min, andmost preferably from about 20 Watts/ft²/min to about 50 Watts/ft²/min.Lower energy corona treatments from about 1 Watts/ft²/min to about 5Watts/ft²/min are also useful but may be less effective. In addition toapplying a charge to the fiber surface, a corona treatment may roughenthe surface by pitting the surface of the fiber.

In a plasma treatment, the fibers, typically as a fiber web, are passedthrough an ionized atmosphere in a chamber that is filled with an inertor non-inert gas, such as oxygen, argon, helium, ammonia, or anotherappropriate inert or non-inert gas, including combinations of the abovegases, to thereby contact the fibers with a combination of neutralmolecules, ions, free radicals, as well as ultraviolet light. At thefiber surfaces, collisions of the surfaces with charged particles (ions)result in both the transfer of kinetic energy and the exchange ofelectrons, etc. In addition, collisions between the surfaces and freeradicals will result in similar chemical rearrangements. Chemicalchanges to the fiber substrate are also caused by bombardment of thefiber surface by ultraviolet light, which is emitted by excited atoms,and by molecules relaxing to lower states.

As a result of these interactions, the plasma treatment may modify boththe chemical structure of the fiber as well as the topography of thefiber surfaces. For example, like corona treatment, a plasma treatmentmay also add polarity to the fiber surface and/or oxidize fiber surfacemoieties. Plasma treatment may also serve to increase the surface energyof the fiber, reduce the contact angle, modify the crosslink density ofthe fiber surface thereby increasing hardness, melting point and themass anchorage of subsequent coatings, and may add a chemicalfunctionality to the fiber surface and potentially ablate the fibersurface. These effects are likewise dependent on the fiber chemistry,and are also dependent on the type of plasma employed.

The selection of gas is important for the desired surface treatmentbecause the chemical structure of the surface is modified differentlyusing different plasma gases. Such would be determined by one skilled inthe art. It is known, for example, that amine functionalities may beintroduced to a fiber surface using ammonia plasma, while carboxyl andhydroxyl groups may be introduced by using oxygen plasma. Accordingly,the reactive atmosphere may comprise one or more of argon, helium,oxygen, nitrogen, ammonia, and/or other gas known to be suitable forplasma treating of fabrics. The reactive atmosphere may comprise one ormore of these gases in atomic, ionic, molecular or free radical form.For example, in a preferred continuous process of the invention, anarray of fibers is passed through a controlled reactive atmosphere thatpreferably comprises argon atoms, oxygen molecules, argon ions, oxygenions, oxygen free radicals, as well as other trace species. In apreferred embodiment, the reactive atmosphere comprises both argon andoxygen at concentrations of from about 90% to about 95% argon and fromabout 5% to about 10% oxygen, with 90/10 or 95/5 concentrations ofargon/oxygen being preferred. In another preferred embodiment, thereactive atmosphere comprises both helium and oxygen at concentrationsof from about 90% to about 95% helium and from about 5% to about 10%oxygen, with 90/10 or 95/5 concentrations of helium/oxygen beingpreferred. Another useful reactive atmosphere is a zero gas atmosphere,i.e. room air comprising about 79% nitrogen, about 20% oxygen and smallamounts of other gases, which is also useful for corona treatment tosome extent.

A plasma treatment differs from a corona treatment mainly in that aplasma treatment is conducted in a controlled, reactive atmosphere ofgases, whereas in corona treatment the reactive atmosphere is air. Theatmosphere in the plasma treater can be easily controlled andmaintained, allowing surface polarity to be achieved in a morecontrollable and flexible manner than corona treating. The electricdischarge is by radio frequency (RF) energy which dissociates the gasinto electrons, ions, free radicals and metastable products. Electronsand free radicals created in the plasma collide with the fiber surface,rupturing covalent bonds and creating free radicals on the fibersurface. In a batch process, after a predetermined reaction time ortemperature, the process gas and RF energy are turned off and theleftover gases and other byproducts are removed. In a continuousprocess, which is preferred herein, an array of fibers is passed througha controlled reactive atmosphere comprising atoms, molecules, ionsand/or free radicals of the selected reactive gases, as well as othertrace species. The reactive atmosphere is constantly generated andreplenished, likely reaching a steady state composition, and is notturned off or quenched until the coating machine is stopped.

Plasma treatment may be carried out using any useful commerciallyavailable plasma treating machine, such as plasma treating machinesavailable from Softal Corona & Plasma GmbH & Co of Hamburg, Germany;4^(th) State, Inc of Belmont Calif.; Plasmatreat US LP of Elgin Ill.;Enercon Surface Treating Systems of Milwaukee, Wis. Plasma treating maybe conducted in a chamber maintained under a vacuum or in a chambermaintained at atmospheric conditions. When atmospheric systems are used,a fully closed chamber is not mandatory. Plasma treating or coronatreating the fibers in a non-vacuum environment, i.e. in a chamber thatis not maintained at either a full or partial vacuum, may increase thepotential for fiber degradation. This is because the concentration ofthe reactive species is proportional to the treatment pressure. Thisincreased potential for fiber degradation may be countered by reducingthe residence time in the treatment chamber. Treating fibers under avacuum, coupled with the need to treat fibers through their fibersurface finish, results in the need for long treatment residence times.This undesirably causes a typical loss of fiber strength properties,such as fiber tenacity, of approximately 15% to 20%. The aggressivenessof the treatments may be reduced by reducing energy flux of thetreatment, but this sacrifices the effectiveness of the treatments inenhancing bonding of adsorbates on the fibers, which limits improvementsin BFS. However, it has also been unexpectedly found that whenconducting the fiber treatments after at least partially removing thefiber finish, fiber tenacity loss is less than 5%, typically less than2% or less than 1%, often no loss at all, and in some instances fiberstrength properties actually increase, which is due to increasedcrosslink density of the polymeric fiber due to the direct treatment ofthe fiber surfaces. When conducting the fiber treatments after at leastpartially removing the fiber finish, the treatments are much moreeffective and may be conducted in less aggressive, non-vacuumenvironments at various levels of energy flux without sacrificingcoating bond enhancement and BFS. In the most preferred embodiments ofthe invention, the high tenacity fibers are subjected to a plasmatreatment or to a corona treatment in a chamber maintained at aboutatmospheric pressure or above atmospheric pressure. As a secondarybenefit, plasma treatment under atmospheric pressure allows thetreatment of more than one fiber at a time, whereas treatment under avacuum is limited to the treatment of one fiber at a time.

A preferred plasma treating process is conducted at about atmosphericpressure, i.e. 1 atm (760 mm Hg (760 torr)), with a chamber temperatureof about room temperature (70° F.-72° F.). The temperature inside theplasma chamber may potentially change due to the treating process, butthe temperature is generally not independently cooled or heated duringtreatments, and it is not believed to affect the treatment of the fibersas they rapidly pass through the plasma treater. The temperature betweenthe plasma electrodes and the fiber web is typically approximately 100°C. The plasma treating process is preferably conducted under RF power atabout 0.5 kW to about 3.5 kW, more preferably from about 1.0 kW to about3.05 kW, and most preferably plasma treating is conducted using anatmospheric plasma treater set at 2.0 kW. This power is distributed overthe width of the plasma treating zone (or the length of the electrodes)and this power is also distributed over the length of the substrate orfiber web at a rate that is inversely proportional to the line speed atwhich the fiber web passes through the reactive atmosphere of the plasmatreater. This energy per unit area per unit time (watts per square footper minute or W/ft²/min) or energy flux, is a useful way to comparetreatment levels. Effective values for energy flux are preferably fromabout 0.5 to about 200 W/ft²/min, more preferably from about 1 to about100 W/ft²/min, even more preferably from about 1 to about 80 W/ft²/min,even more preferably from about 2 to about 40 W/ft²/min, and mostpreferably from about 2 to about 20 W/ft²/min. The total gas flow rateis approximately 16 liters/min, but this is not intended to be strictlylimiting.

As the total gas flow rate is distributed over the width of the plasmatreating zone, additional gas flow may be necessary with increases tothe length/width of the plasma treating zone of the plasma treater. Forexample, a plasma treater having a treating zone width of 2× may needtwice as much gas flow compared to a plasma treater having a treatingzone width of 1×. The plasma treatment time (or residence time) of thefiber is also is relative to the dimensions of the plasma treateremployed and is not intended to be strictly limiting. In a preferredatmospheric system, the fibers are exposed to the plasma treatment witha residence time of from about ½ second to about three seconds, with anaverage residence time of approximately 2 seconds. A more appropriatemeasure is the amount of plasma treatment in terms of RF power appliedto the fiber per unit area over time.

Additionally, composites and fabrics of the invention may comprise somefibers that are treated and some fibers that are not treated. Forexample, composites herein may be fabricated from some fibers that arecorona treated and some fibers that are plasma treated. Each of theseexemplary processes, through their action on the surface of the fiber,can be employed to modify, improve or reduce the interaction between thebulk fiber and subsequent coating materials, depending on fiberchemistry. The various treatment steps of the invention may be utilizedas a recipe for manipulating the fibers in order to place the compositewithin the desired range for backface signature or other properties. IfBFS testing determines that a particular composite has a worse BFS thandesired, that is indicative that further fiber washing and/or furthersurface treatment should be conducted to further increase saidproperties to fall within the desired range.

The plasma and corona treatments will be conducted after the at leastpartial removal of the fiber surface finish but prior to the applicationof any binder/matrix resins or other surface adsorbates/coatings.Treating the exposed fiber surfaces immediately before coating thealigned fiber web with a polymeric binder material or resin is mostpreferred because it will cause the least disruption to the fibermanufacturing process and will leave the fiber in a modified andunprotected state for the shortest period of time. It is ideal to removethe fiber surface finish and treat the exposed fiber surfacesimmediately after unwinding fibers from a fiber spool (wound fiberpackage) and aligning the fibers into a fiber web, followed byimmediately coating or impregnating the fibers with a polymer/resincoating. This will also leave the fibers in a treated and uncoated statefor the shortest length of time should there be considerations about theshelf-life or decay rate of the surface modification of the fiber.However, this is ideal primarily for causing the least disruption to theoverall fabrication process, and not necessarily for achieving animprovement in BFS performance of the composite.

Fibrous composites produced according to the methods described hereinhave been found to exhibit excellent backface signature properties. Theimprovement in backface signature is particularly evident when thecomponent fibers are polyethylene fibers, which are naturally superiorto other fibers in their ballistic resistance abilities but notnecessarily in their structural properties. Treating the surfaces ofpolyethylene fibers as described above prior to the fabrication ofpolyethylene-based fabrics formed therefrom achieves a combination ofstructural properties, ballistic penetration resistance and backfacesignature resistance properties that are comparatively superior to anyother fiber type, including aramid fibers.

In this regard, the fibrous composites of the invention have a preferredbackface signature of less than about 6 mm as measured for a compositehaving an areal density of 2.0 psf when impacted with a 124-grain, 9 mmFMJ RN projectile fired at a velocity of from about 427 m/s to about 445m/s (1430 feet/second (fps)±30 fps), measured at room temperature. Thisis not to say that all fibrous composites or articles of the inventionwill have an areal density of 2.0 psf, nor that all fibrous compositesor articles of the invention will have a BFS of 6 mm against such an FMJRN projectile at said velocity. Such only identifies that compositesfabricated according to the processes of the invention are characterizedin that when fabricated into a 2.0 psf panel, that 2.0 psf panel willhave a BFS of less than about 6 mm against such an FMJ RN projectile atsaid velocity when measured at approximately room temperature (appx. 70°F.-72° F.).

It should also be understood that the terms BFS, backface deformation,trauma signature and blunt force trauma are not measures of the depth ofdepression of the composite due to projectile impact, but rather aremeasures of the depth of depression in a backing material or into a userbody due to projectile impact. This is particularly relevant for thestudy of hard armor, particularly helmet armor. Helmet BFS is typicallytested by placing a prototype helmet on a metallic head form, where thehelmet is held on the head form by a suspension system that separatesthe helmet from the head form by ½ inch (1.27 cm). Sections of the headform are filled with clay, and the depth of depression in those clayareas is measured as the BFS without including the ½ inch spacing depthin the measurement. This is done for the purpose of correlating thelaboratory BFS testing with actual BFS experienced by a soldier in fielduse, where a typical helmet incorporates a typical ½ inch offset fromthe head, due to helmet interior padding or a suspensionsystem/retention harness. The BFS of soft armor, on the other hand, isconventionally tested by placing the armor directly on the clay surfacewith no spacing, which is consistent with its position in actual fielduse. Accordingly, BFS depth measurements are relative to the test methodused, and when comparing BFS depth measurements, it is necessary toidentify whether or not the test method used required positioning thetest sample directly on a backing material or spaced from the backingmaterial. In this regard, all backface signature data in thisapplication was measured using an apparatus described in patentapplication Ser. No. 61/531,233 with a ½ inch space between the 2.0 psfsample and a clay backing material. In the preferred embodiments of theinvention, the fibrous composites of the invention have a more preferredbackface signature of less than about 5 mm when impacted with a124-grain, 9 mm FMJ projectile fired at a velocity of from about 427 m/sto about 445 m/s under the projectile firing conditions of NIJ Standard0101.04, more preferably less than about 4 mm, more preferably less thanabout 3 mm, more preferably less than about 2 mm, and most preferablyhave a backface signature of less than about 1 mm when impacted with a124-grain, 9 mm FMJ RN projectile (a bullet comprising approximately 90%copper and 10% zinc excluding the base) fired at a velocity of fromabout 427 m/s to about 445 m/s, when measured approximately at roomtemperature. Testing BFS against a 124-grain, 9 mm FMJ RN projectilefired at a velocity of from about 427 m/s to about 445 m/s is common inthe art.

Said fibrous composites achieving these BFS values each comprise aplurality of adjoined fiber layers, each fiber layer comprising fibershaving surfaces that are at least partially covered with a polymericmaterial, wherein said fibers are predominantly free of a fiber surfacefinish such that said polymeric material is predominantly in directcontact with the fiber surfaces. Said fibrous composites achieving theseBFS values also preferably exhibit a V₅₀ against a 16-grain RightCircular Cylinder (RCC) projectile of at least about 3200 feet/sec (fps)(975.36 m/s), more preferably at least about 3300 fps (1005.84 m/s),even more preferably at least about 3400 fps (1036.32 m/s), still morepreferably at least about 3500 fps (1066.8 m/s) and most preferably atleast about 3600 fps (1097.28 m/s). All of the above V₅₀ values are forarmor panels having a composite areal density of approximately 2.0lbs/ft² (psf) (9.76 kg/m² (ksm)). As with BFS, this is not to say thatall fibrous composites or articles of the invention will have aparticular areal density, nor that all fibrous composites or articles ofthe invention will have a V₅₀ against a 16-grain RCC projectile of atleast about 3300 feet/sec. Such only identifies that compositesfabricated according to the processes of the invention are characterizedin that when fabricated into a 2.0 psf panel, that 2.0 psf panel willhave a V₅₀ against a 16-grain RCC projectile of at least about 3200feet/sec.

In a preferred embodiment of the invention, the fibrous composites ofthe invention have a V₅₀ against a 16-grain RCC projectile of at leastabout 3200 fps or at least about 3300 fps in addition to a BFS of about5 mm or less against a 124-grain, 9 mm FMJ RN projectile fired at avelocity of from about 427 m/s to about 445 m/s, more preferably a V₅₀against a 16-grain RCC projectile of at least about 3200 fps or at leastabout 3300 fps in addition to a BFS of about 4 mm or less against a124-grain, 9 mm FMJ RN projectile fired at a velocity of from about 427m/s to about 445 m/s, and still more preferably a V₅₀ against a 16-grainRCC projectile of at least about 3200 fps or at least about 3300 fps inaddition to a BFS of about 3 mm or less, about 2 mm or less, or about 1mm or less against a 124-grain, 9 mm FMJ RN projectile fired at avelocity of from about 427 m/s to about 445 m/s, when measuredapproximately at room temperature. In a more preferred embodiment of theinvention, the fibrous composites of the invention have a V₅₀ against a16-grain RCC projectile of at least about 3400 fps or at least about3500 fps in addition to a BFS of about 5 mm or less against a 124-grain,9 mm FMJ RN projectile fired at a velocity of from about 427 m/s toabout 445 m/s, more preferably a V₅₀ against a 16-grain RCC projectileof at least about 3400 fps or at least about 3500 fps in addition to aBFS of about 4 mm or less against a 124-grain, 9 mm FMJ RN projectilefired at a velocity of from about 427 m/s to about 445 m/s, and mostpreferably a V₅₀ against a 16-grain RCC projectile of at least about3300 fps in addition to a BFS of about 3 mm or less, about 2 mm or less,or about 1 mm or less against a 124-grain, 9 mm FMJ RN projectile firedat a velocity of from about 427 m/s to about 445 m/s, when measuredapproximately at room temperature. In a most preferred embodiment of theinvention, the fibrous composites of the invention have a V₅₀ against a16-grain RCC projectile of at least about 3600 fps in addition to a BFSof about 5 mm or less against a 124-grain, 9 mm FMJ RN projectile firedat a velocity of from about 427 m/s to about 445 m/s, more preferably aV₅₀ against a 16-grain RCC projectile of at least about 3600 fps inaddition to a BFS of about 4 mm or less against a 124-grain, 9 mm FMJ RNprojectile fired at a velocity of from about 427 m/s to about 445 m/s,and most preferably a V₅₀ against a 16-grain RCC projectile of at leastabout 3600 fps in addition to a BFS of about 3 mm or less, about 2 mm orless, or about 1 mm or less against a 124-grain, 9 mm FMJ RN projectilefired at a velocity of from about 427 m/s to about 445 m/s, whenmeasured approximately at room temperature. As previously, this BFS datawas measured using an apparatus described in patent application Ser. No.61/531,233 with a ½ inch space between the 2.0 psf sample and a claybacking material, measured at room temperature.

The high-strength, high tensile modulus polymeric fibers forming thefiber layers and composites of the invention may be of any fibertenacity provided that the fiber tenacity after plasma/corona treatingis from about 95% to 100% of the original fiber tenacity prior toplasma/corona treating (i.e. fiber tenacity loss due to treatment isless than 5%), more preferably is from about 98% to 100% of the originalfiber tenacity (i.e. fiber tenacity loss due to treatment is less than2%), still more preferably is from about 99% to 100% of the originalfiber tenacity (i.e. fiber tenacity loss due to treatment is less than1%), still more preferably wherein the fiber tenacity afterplasma/corona treating is equal to the original fiber tenacity beforeplasma/corona treating (i.e. no fiber tenacity loss due to treatment),and most preferably wherein the fiber tenacity after plasma/coronatreating is greater than the original fiber tenacity prior toplasma/corona treating (i.e. fiber tenacity increase due to treatment).

Accordingly, the fiber layers and composites formed herein arepreferably ballistic resistant composites formed from high-strength,high tensile modulus polymeric fibers having a tenacity prior toplasma/corona treating of at least about 20 g/denier as well as atenacity after plasma/corona treating of at least about 20 g/denier.More preferably, the fibers have a tenacity prior to plasma/coronatreating of at least about 25 g/denier as well as a tenacity afterplasma/corona treating of at least about 25 g/denier. More preferably,the fibers have a tenacity prior to plasma/corona treating of at leastabout 30 g/denier as well as a tenacity after plasma/corona treating ofat least about 30 g/denier. More preferably, the fibers have a tenacityprior to plasma/corona treating of at least about 33 g/denier as well asa tenacity after plasma/corona treating of at least about 33 g/denier.More preferably, the fibers have a tenacity prior to plasma/coronatreating of at least about 35 g/denier as well as a tenacity afterplasma/corona treating of at least about 35 g/denier. Still morepreferably, the fibers have a tenacity prior to plasma/corona treatingof at least about 37 g/denier as well as a tenacity after plasma/coronatreating of at least about 37 g/denier. More preferably, the fibers havea tenacity prior to plasma/corona treating of at least about 39 g/denieras well as a tenacity after plasma/corona treating of at least about 39g/denier. More preferably, the fibers have a tenacity prior toplasma/corona treating of at least about 45 g/denier as well as atenacity after plasma/corona treating of at least about 45 g/denier.More preferably, the fibers have a tenacity prior to plasma/coronatreating of at least about 50 g/denier as well as a tenacity afterplasma/corona treating of at least about 50 g/denier. More preferably,the fibers have a tenacity prior to plasma/corona treating of at leastabout 55 g/denier as well as a tenacity after plasma/corona treating ofat least about 55 g/denier. Still more preferably, the fibers have atenacity prior to plasma/corona treating of at least about 60 g/denieras well as a tenacity after plasma/corona treating of at least about 60g/denier. Most preferably, the fibers have a tenacity prior toplasma/corona treating of at least about 65 g/denier as well as atenacity after plasma/corona treating of at least about 65 g/denier. Alltenacity measurements identified herein are measured at ambient roomtemperature. As used herein, the term “denier” refers to the unit oflinear density, equal to the mass in grams per 9000 meters of fiber oryarn. As used herein, the term “tenacity” refers to the tensile stressexpressed as force (grams) per unit linear density (denier) of anunstressed specimen and is measured by ASTM D2256. The “initial modulus”of a fiber is the property of a material representative of itsresistance to deformation. The term “tensile modulus” refers to theratio of the change in tenacity, expressed in grams-force per denier(g/d) to the change in strain, expressed as a fraction of the originalfiber length (in/in). The tensile modulus of fibers is also affected bythe plasma and corona treatments like the fiber tenacity. However,plasma or corona treating the fibers under atmospheric pressure afterremoving the fiber surface finish has actually been found to raise themodulus due to an increase in crosslink density due to the directtreatment of the fiber surfaces.

The polymers forming the fibers are preferably high-strength, hightensile modulus fibers suitable for the manufacture of ballisticresistant composites/fabrics. Particularly suitable high-strength, hightensile modulus fiber materials that are particularly suitable for theformation of ballistic resistant composites and articles includepolyolefin fibers, including high density and low density polyethylene.Particularly preferred are extended chain polyolefin fibers, such ashighly oriented, high molecular weight polyethylene fibers, particularlyultra-high molecular weight polyethylene fibers, and polypropylenefibers, particularly ultra-high molecular weight polypropylene fibers.Also suitable are aramid fibers, particularly para-aramid fibers,polyamide fibers, polyethylene terephthalate fibers, polyethylenenaphthalate fibers, extended chain polyvinyl alcohol fibers, extendedchain polyacrylonitrile fibers, polybenzazole fibers, such aspolybenzoxazole (PBO) and polybenzothiazole (PBT) fibers, liquid crystalcopolyester fibers and other rigid rod fibers such as M5® fibers. Eachof these fiber types is conventionally known in the art. Also suitablefor producing polymeric fibers are copolymers, block polymers and blendsof the above materials.

The most preferred fiber types for ballistic resistant fabrics includepolyethylene, particularly extended chain polyethylene fibers, aramidfibers, polybenzazole fibers, liquid crystal copolyester fibers,polypropylene fibers, particularly highly oriented extended chainpolypropylene fibers, polyvinyl alcohol fibers, polyacrylonitrile fibersand other rigid rod fibers, particularly M5® fibers. Specifically mostpreferred fibers are aramid fibers.

In the case of polyethylene, preferred fibers are extended chainpolyethylenes having molecular weights of at least 500,000, preferablyat least one million and more preferably between two million and fivemillion. Such extended chain polyethylene (ECPE) fibers may be grown insolution spinning processes such as described in U.S. Pat. No. 4,137,394or 4,356,138, which are incorporated herein by reference, or may be spunfrom a solution to form a gel structure, such as described in U.S. Pat.Nos. 4,551,296 and 5,006,390, which are also incorporated herein byreference. A particularly preferred fiber type for use in the inventionare polyethylene fibers sold under the trademark SPECTRA® from HoneywellInternational Inc. SPECTRA® fibers are well known in the art and aredescribed, for example, in U.S. Pat. Nos. 4,623,547 and 4,748,064. Inaddition to polyethylene, another useful polyolefin fiber type ispolypropylene (fibers or tapes), such as TEGRIS® fibers commerciallyavailable from Milliken & Company of Spartanburg, S.C.

Also particularly preferred are aramid (aromatic polyamide) orpara-aramid fibers. Such are commercially available and are described,for example, in U.S. Pat. No. 3,671,542. For example, usefulpoly(p-phenylene terephthalamide) filaments are produced commercially byDuPont under the trademark of KEVLAR®. Also useful in the practice ofthis invention are poly(m-phenylene isophthalamide) fibers producedcommercially by DuPont under the trademark NOMEX® and fibers producedcommercially by Teijin under the trademark TWARON®; aramid fibersproduced commercially by Kolon Industries, Inc. of Korea under thetrademark HERACRON®; p-aramid fibers SVM™ and RUSAR™ which are producedcommercially by Kamensk Volokno JSC of Russia and ARIVIOS™ p-aramidfibers produced commercially by JSC Chim Volokno of Russia.

Suitable polybenzazole fibers for the practice of this invention arecommercially available and are disclosed for example in U.S. Pat. Nos.5,286,833, 5,296,185, 5,356,584, 5,534,205 and 6,040,050, each of whichis incorporated herein by reference. Suitable liquid crystal copolyesterfibers for the practice of this invention are commercially available andare disclosed, for example, in U.S. Pat. Nos. 3,975,487; 4,118,372 and4,161,470, each of which is incorporated herein by reference. Suitablepolypropylene fibers include highly oriented extended chainpolypropylene (ECPP) fibers as described in U.S. Pat. No. 4,413,110,which is incorporated herein by reference. Suitable polyvinyl alcohol(PV-OH) fibers are described, for example, in U.S. Pat. Nos. 4,440,711and 4,599,267 which are incorporated herein by reference. Suitablepolyacrylonitrile (PAN) fibers are disclosed, for example, in U.S. Pat.No. 4,535,027, which is incorporated herein by reference. Each of thesefiber types is conventionally known and is widely commerciallyavailable.

M5® fibers are formed frompyridobisimidazole-2,6-diyl(2,5-dihydroxy-p-phenylene) and aremanufactured by Magellan Systems International of Richmond, Va. and aredescribed, for example, in U.S. Pat. Nos. 5,674,969, 5,939,553,5,945,537, and 6,040,478, each of which is incorporated herein byreference. Also suitable are combinations of all the above materials,all of which are commercially available. For example, the fibrous layersmay be formed from a combination of one or more of aramid fibers, UHMWPEfibers (e.g. SPECTRA® fibers), carbon fibers, etc., as well asfiberglass and other lower-performing materials. However, BFS and V₅₀values may vary by fiber type.

The fibers may be of any suitable denier useful to achieve fibers havingtenacities as defined above. The selection is governed by considerationsof ballistic effectiveness and cost. Finer fibers are more costly tomanufacture and to weave, but can produce greater ballisticeffectiveness per unit weight. Ultra high molecular weight polyethylenefibers having a tenacity of at least about 37 g/denier are obtainable,for example, by employing the process of application Ser. No.13/173,919, filed Jun. 30, 2011.

Other known processes for the manufacture of high strength fibers aredisclosed in, for example, U.S. Pat. Nos. 4,413,110, 4,440,711,4,535,027, 4,457,985, 4,623,547 4,650,710 and 4,748,06, which areincorporated herein by reference to the extent consistent herewith. Suchmethods, including solution grown or gel fiber processes, are well knownin the art. Methods of forming each of the other preferred fiber types,including para-aramid fibers, are also conventionally known in the art,and the fibers are commercially available.

After removing at least a portion of the fiber surface finish from thefiber surfaces as desired, and after the fiber surfaces are optionallytreated under conditions effective to enhance the adsorbability of asubsequently applied adsorbate on the fiber surfaces, an adsorbate isthen optionally applied onto at least a portion of at least some of thefibers. To this end, an “adsorbate” may be any solid, liquid or gas,including polymeric binder materials and resins, and adsorption includesany form of bonding of the materials to the fiber surfaces. Thedefinition of “adsorbate” expressly includes all polymers useful aspolymer binder materials, resins or polymeric matrix materials, but theclass of useful adsorbates expressly excludes materials that do not havebinding properties, including fiber surface finish substances such as aspin finish materials, which are not binder materials having bindingproperties. To the contrary, fiber surface finish materials arespecifically removed from fiber surfaces according to the invention. Theterm “adsorbate” also expressly includes inorganic materials, such assilicon oxide, titanium oxide, aluminum oxide, tantalum oxide, hafniumoxide, zirconium oxide, titanium aluminate, titanium silicate, hafniumaluminate, hafnium silicate, zirconium aluminate, zirconium silicate,boron nitride or a combination thereof, as are disclosed incommonly-owned U.S. patent application publication no. 2008/0119098, thedisclosure of which is incorporated herein by reference.

The term “adsorption” (or “adsorbability” or “adsorb”) is broadlyintended to encompass both physisorption and chemisorption of anymaterial (solid, liquid, gas or plasma) on the fiber surface, where“physisorption” is defined herein as physical bonding of a material on afiber surface and “chemisorption” is defined herein as chemical bondingof a material on a fiber surface, where a chemical reaction occurs atthe exposed fiber (i.e. the adsorbant) surface. The term “adsorption” asused herein is intended to include any possible means of attaching,adhering or bonding a material to a substrate surface, physically orchemically, without limitation, including means for increasing fiberwetting/adhesion of fibers in polymer matrices. This expressly includesthe adhesion or coating of any solid, liquid or gas material on thefiber surfaces, including any monomer, oligomer, polymer or resin, andincluding the application of any organic material or inorganic materialonto the fiber surfaces.

It is most preferred herein that the fibers forming the woven ornon-woven materials of the invention are coated with or impregnated witha polymeric binder material. The polymeric binder material adsorbate,such as a resin, either partially or substantially coats the individualfibers of the fiber layers, preferably substantially coating each of theindividual fibers of each fiber layer. The polymeric binder material isalso commonly known in the art as a “polymeric matrix” material, andthese terms are used interchangeably herein. These terms areconventionally known in the art and describe a material that bindsfibers together either by way of its inherent adhesive characteristicsor after being subjected to well known heat and/or pressure conditions.Such a “polymeric matrix” or “polymeric binder” material may alsoprovide a fabric with other desirable properties, such as abrasionresistance and resistance to deleterious environmental conditions, so itmay be desirable to coat the fibers with such a binder material evenwhen its binding properties are not important, such as with wovenfabrics.

Suitable polymeric binder materials include both low modulus,elastomeric materials and high modulus, rigid materials. As used hereinthroughout, the term tensile modulus means the modulus of elasticity asmeasured by ASTM 2256 for a fiber and by ASTM D638 for a polymericbinder material. A low or high modulus binder may comprise a variety ofpolymeric and non-polymeric materials. A preferred polymeric bindercomprises a low modulus elastomeric material. For the purposes of thisinvention, a low modulus elastomeric material has a tensile modulusmeasured at about 6,000 psi (41.4 MPa) or less according to ASTM D638testing procedures. A low modulus polymer preferably has, the tensilemodulus of the elastomer is about 4,000 psi (27.6 MPa) or less, morepreferably about 2400 psi (16.5 MPa) or less, more preferably 1200 psi(8.23 MPa) or less, and most preferably is about 500 psi (3.45 MPa) orless. The glass transition temperature (Tg) of the elastomer ispreferably less than about 0° C., more preferably the less than about−40° C., and most preferably less than about −50° C. The elastomer alsohas a preferred elongation to break of at least about 50%, morepreferably at least about 100% and most preferably has an elongation tobreak of at least about 300%.

A wide variety of materials and formulations having a low modulus may beutilized as the polymeric binder. Representative examples includepolybutadiene, polyisoprene, natural rubber, ethylene-propylenecopolymers, ethylene-propylene-diene terpolymers, polysulfide polymers,polyurethane elastomers, chlorosulfonated polyethylene, polychloroprene,plasticized polyvinylchloride, butadiene acrylonitrile elastomers,poly(isobutylene-co-isoprene), polyacrylates, polyesters, polyethers,fluoroelastomers, silicone elastomers, copolymers of ethylene,polyamides (useful with some fiber types), acrylonitrile butadienestyrene, polycarbonates, and combinations thereof, as well as other lowmodulus polymers and copolymers curable below the melting point of thefiber. Also preferred are blends of different elastomeric materials, orblends of elastomeric materials with one or more thermoplastics.

Particularly useful are block copolymers of conjugated dienes and vinylaromatic monomers. Butadiene and isoprene are preferred conjugated dieneelastomers. Styrene, vinyl toluene and t-butyl styrene are preferredconjugated aromatic monomers. Block copolymers incorporatingpolyisoprene may be hydrogenated to produce thermoplastic elastomershaving saturated hydrocarbon elastomer segments. The polymers may besimple tri-block copolymers of the type A-B-A, multi-block copolymers ofthe type (AB)_(n) (n=2-10) or radial configuration copolymers of thetype R-(BA)_(x) (x=3-150); wherein A is a block from a polyvinylaromatic monomer and B is a block from a conjugated diene elastomer.Many of these polymers are produced commercially by Kraton Polymers ofHouston, Tex. and described in the bulletin “Kraton ThermoplasticRubber”, SC-68-81. Also useful are resin dispersions ofstyrene-isoprene-styrene (SIS) block copolymer sold under the trademarkPRINLIN® and commercially available from Henkel Technologies, based inDüsseldorf, Germany. Particularly preferred low modulus polymeric binderpolymers comprise styrenic block copolymers sold under the trademarkKRATON® commercially produced by Kraton Polymers. A particularlypreferred polymeric binder material comprises apolystyrene-polyisoprene-polystyrene-block copolymer sold under thetrademark KRATON®.

While low modulus polymeric matrix binder materials are most useful forthe formation of flexible armor, such as ballistic resistant vests, highmodulus, rigid materials useful for forming hard armor articles, such ashelmets, are particularly preferred herein. Preferred high modulus,rigid materials generally have a higher initial tensile modulus than6,000 psi. Preferred high modulus, rigid polymeric binder materialsuseful herein include polyurethanes (both ether and ester based),epoxies, polyacrylates, phenolic/polyvinyl butyral (PVB) polymers, vinylester polymers, styrene-butadiene block copolymers, as well as mixturesof polymers such as vinyl ester and diallyl phthalate or phenolformaldehyde and polyvinyl butyral. A particularly preferred rigidpolymeric binder material for use in this invention is a thermosettingpolymer, preferably soluble in carbon-carbon saturated solvents such asmethyl ethyl ketone, and possessing a high tensile modulus when cured ofat least about 1×10⁶ psi (6895 MPa) as measured by ASTM D638.Particularly preferred rigid polymeric binder materials are thosedescribed in U.S. Pat. No. 6,642,159, the disclosure of which isincorporated herein by reference. The polymeric binder, whether a lowmodulus material or a high modulus material, may also include fillerssuch as carbon black or silica, may be extended with oils, or may bevulcanized by sulfur, peroxide, metal oxide or radiation cure systems asis well known in the art.

Most specifically preferred are polar resins or polar polymers,particularly polyurethanes within the range of both soft and rigidmaterials at a tensile modulus ranging from about 2,000 psi (13.79 MPa)to about 8,000 psi (55.16 MPa). Preferred polyurethanes are applied asaqueous polyurethane dispersions that are most preferably, but notnecessarily, cosolvent free. Such includes aqueous anionic polyurethanedispersions, aqueous cationic polyurethane dispersions and aqueousnonionic polyurethane dispersions. Particularly preferred are aqueousanionic polyurethane dispersions; aqueous aliphatic polyurethanedispersions, and most preferred are aqueous anionic, aliphaticpolyurethane dispersions, all of which are preferably cosolvent freedispersions. Such includes aqueous anionic polyester-based polyurethanedispersions; aqueous aliphatic polyester-based polyurethane dispersions;and aqueous anionic, aliphatic polyester-based polyurethane dispersions,all of which are preferably cosolvent free dispersions. Such alsoincludes aqueous anionic polyether polyurethane dispersions; aqueousaliphatic polyether-based polyurethane dispersions; and aqueous anionic,aliphatic polyether-based polyurethane dispersions, all of which arepreferably cosolvent free dispersions. Similarly preferred are allcorresponding variations (polyester-based; aliphatic polyester-based;polyether-based; aliphatic polyether-based, etc.) of aqueous cationicand aqueous nonionic dispersions. Most preferred is an aliphaticpolyurethane dispersion having a modulus at 100% elongation of about 700psi or more, with a particularly preferred range of 700 psi to about3000 psi. More preferred are aliphatic polyurethane dispersions having amodulus at 100% elongation of about 1000 psi or more, and still morepreferably about 1100 psi or more. Most preferred is an aliphatic,polyether-based anionic polyurethane dispersion having a modulus of 1000psi or more, preferably 1100 psi or more.

The rigidity, impact and ballistic properties of the articles formedfrom the composites of the invention are affected by the tensile modulusof the polymeric binder polymer coating the fibers. For example, U.S.Pat. No. 4,623,574 discloses that fiber reinforced compositesconstructed with elastomeric matrices having tensile moduli less thanabout 6,000 psi (41,300 kPa) have superior ballistic properties comparedboth to composites constructed with higher modulus polymers, and alsocompared to the same fiber structure without a polymeric bindermaterial. However, low tensile modulus polymeric binder materialpolymers also yield lower rigidity composites. Further, in certainapplications, particularly those where a composite must function in bothanti-ballistic and structural modes, there is needed a superiorcombination of ballistic resistance and rigidity. Accordingly, the mostappropriate type of polymeric binder polymer to be used will varydepending on the type of article to be formed from the composites of theinvention. In order to achieve a compromise in both properties, asuitable polymeric binder may combine both low modulus and high modulusmaterials to form a single polymeric binder.

The polymeric binder material may be applied either simultaneously orsequentially to a plurality of fibers arranged as a fiber web (e.g. aparallel array or a felt) to form a coated web, applied to a wovenfabric to form a coated woven fabric, or as another arrangement, tothereby impregnate the fiber layers with the binder. As used herein, theterm “impregnated with” is synonymous with “embedded in” as well as“coated with” or otherwise applied with the coating where the bindermaterial diffuses into the fiber layer and is not simply on a surface ofthe fiber layers. The polymeric material may also be applied onto atleast one array of fibers that is not part of a fiber web, followed byweaving the fibers into a woven fabric or followed by formulating anon-woven fabric following the methods described previously herein.Techniques of forming woven and non-woven fiber plies, layers andfabrics are well known in the art.

Although not required, fibers forming woven fiber layers are at leastpartially coated with a polymeric binder, followed by a consolidationstep similar to that conducted with non-woven fiber layers. Such aconsolidation step may be conducted to merge multiple woven fiber layerswith each other, or to further merge the binder with the fibers of saidwoven fabric. For example, a plurality of woven fiber layers do notnecessarily have to be consolidated, and may be attached by other means,such as with a conventional adhesive, or by stitching.

Generally, a polymeric binder coating is necessary to efficiently merge,i.e. consolidate, a plurality of non-woven fiber plies. The polymericbinder material may be applied onto the entire surface area of theindividual fibers or only onto a partial surface area of the fibers.Most preferably, the coating of the polymeric binder material is appliedonto substantially all the surface area of each individual fiber forminga fiber layer of the invention. Where a fiber layer comprises aplurality of yarns, each fiber forming a single strand of yarn ispreferably coated with the polymeric binder material.

Any appropriate application method may be utilized to apply thepolymeric binder material and the term “coated” is not intended to limitthe method by which it is applied onto the filaments/fibers. Thepolymeric binder material is applied directly onto the fiber surfacesusing any appropriate method that would be readily determined by oneskilled in the art, and the binder then typically diffuses into thefiber layer as discussed herein. Most preferably, a method is used whichat least partially coats each individual fiber with the polymericmaterial, preferably substantially coating or encapsulating each of theindividual fibers and covering all or substantially all of thefilament/fiber surface area with the polymeric binder material.

While it is necessary that the fibers be coated with a polymeric binderafter the at least partial removal of the fiber surface finish, andpreferably after a surface treatment that enhances the adsorbability ofa subsequently applied adsorbate on the fiber surfaces, the fibers maybe coated with the polymeric binder either before or after the fibersare arranged into one or more plies/layers, or before or after thefibers are woven into a woven fabric. Woven fabrics may be formed usingtechniques that are well known in the art using any fabric weave, suchas plain weave, crowfoot weave, basket weave, satin weave, twill weaveand the like. Plain weave is most common, where fibers are woventogether in an orthogonal 0°/90° orientation. Either prior to or afterweaving, the individual fibers of each woven fabric material may or maynot be coated with the polymeric binder material. Typically, weaving offabrics is performed prior to coating fibers with the polymeric binder,where the woven fabrics are thereby impregnated with the binder.However, the invention is not intended to be limited by the stage atwhich the polymeric binder is applied to the fibers, nor by the meansused to apply the polymeric binder.

Methods for the production of non-woven fabrics are well known in theart. In the preferred embodiments herein, a plurality of fibers arearranged into at least one array, typically being arranged as a fiberweb comprising a plurality of fibers aligned in a substantiallyparallel, unidirectional array. As previously stated, in a typicalprocess for forming non-woven unidirectionally aligned fiber plies,fiber bundles are supplied from a creel and led through guides and oneor more spreader bars into a collimating comb, followed by coating thefibers with a polymeric binder material. A typical fiber bundle willhave from about 30 to about 2000 individual fibers. The spreader barsand collimating comb disperse and spread out the bundled fibers,reorganizing them side-by-side in a coplanar fashion. Ideal fiberspreading results in the individual filaments or individual fibers beingpositioned next to one another in a single fiber plane, forming asubstantially unidirectional, parallel array of fibers without fibersoverlapping each other. At this point, removing the fiber surface finishbefore or during this spreading step may enhance and accelerate thespreading of the fibers into such a parallel array.

After the fibers are coated with the binder material, the coated fibersare formed into non-woven fiber layers that comprise a plurality ofoverlapping, non-woven fiber plies that are consolidated into asingle-layer, monolithic element. In a preferred non-woven fabricstructure of the invention, a plurality of stacked, overlapping unitapesare formed wherein the parallel fibers of each single ply (unitape) arepositioned orthogonally to the parallel fibers of each adjacent singleply relative to the longitudinal fiber direction of each single ply. Thestack of overlapping non-woven fiber plies is consolidated under heatand pressure, or by adhering the coatings of individual fiber plies, toform a single-layer, monolithic element which has also been referred toin the art as a single-layer, consolidated network where a “consolidatednetwork” describes a consolidated (merged) combination of fiber plieswith the polymeric matrix/binder. Articles of the invention may alsocomprise hybrid consolidated combinations of adjoined woven fabrics andnon-woven fabrics, as well as combinations of non-woven fabrics formedfrom unidirectional fiber plies and non-woven felt fabrics.

Most typically, non-woven fiber layers or fabrics include from 1 toabout 6 adjoined fiber plies, but may include as many as about 10 toabout 20 plies as may be desired for various applications. The greaterthe number of plies translates into greater ballistic resistance, butalso greater weight. Accordingly, the number of fiber plies forming afiber layer composite and/or fabric composite or an article of theinvention varies depending upon the ultimate use of the fabric orarticle. For example, in body armor vests for military applications, inorder to form an article composite that achieves a desired 1.0 pound persquare foot or less areal density (4.9 kg/m²), a total of about 100plies (or layers) to about 50 individual plies (or layers) may berequired, wherein the plies/layers may be woven, knitted, felted ornon-woven fabrics (with parallel oriented fibers or other arrangements)formed from the high-strength fibers described herein. In anotherembodiment, body armor vests for law enforcement use may have a numberof plies/layers based on the NIJ threat level. For example, for an NIJthreat level IIIA vest, there may be a total of 40 plies. For a lowerNIJ threat level, fewer plies/layers may be employed. The inventionallows for the incorporation of a greater number of fiber plies toachieve the desired level of ballistic protection without increasing thefabric weight as compared to other known ballistic resistant structures.

As is conventionally known in the art, excellent ballistic resistance isachieved when individual fiber plies are cross-plied such that the fiberalignment direction of one ply is rotated at an angle with respect tothe fiber alignment direction of another ply. Most preferably, the fiberplies are cross-plied orthogonally at 0° and 90° angles, but adjacentplies can be aligned at virtually any angle between about 0° and about90° with respect to the longitudinal fiber direction of another ply. Forexample, a five ply non-woven structure may have plies oriented at a0°/45°/90°/45°/0° or at other angles. Such rotated unidirectionalalignments are described, for example, in U.S. Pat. Nos. 4,457,985;4,748,064; 4,916,000; 4,403,012; 4,623,574; and 4,737,402, all of whichare incorporated herein by reference to the extent not incompatibleherewith.

Methods of consolidating fiber plies to form fiber layers and compositesare well known, such as by the methods described in U.S. Pat. No.6,642,159. Consolidation can occur via drying, cooling, heating,pressure or a combination thereof. Heat and/or pressure may not benecessary, as the fibers or fabric layers may just be glued together, asis the case in a wet lamination process. Typically, consolidation isdone by positioning the individual fiber plies on one another underconditions of sufficient heat and pressure to cause the plies to combineinto a unitary fabric. Consolidation may be done at temperatures rangingfrom about 50° C. to about 175° C., preferably from about 105° C. toabout 175° C., and at pressures ranging from about 5 psig (0.034 MPa) toabout 2500 psig (17 MPa), for from about 0.01 seconds to about 24 hours,preferably from about 0.02 seconds to about 2 hours. When heating, it ispossible that the polymeric binder coating can be caused to stick orflow without completely melting. However, generally, if the polymericbinder material (if it is one that is capable of melting) is caused tomelt, relatively little pressure is required to form the composite,while if the binder material is only heated to a sticking point, morepressure is typically required. As is conventionally known in the art,consolidation may be conducted in a calender set, a flat-bed laminator,a press or in an autoclave. Most commonly, a plurality of orthogonalfiber webs are “glued” together with the binder polymer and run througha flat bed laminator to improve the uniformity and strength of the bond.Further, the consolidation and polymer application/bonding steps maycomprise two separate steps or a single consolidation/lamination step.

Alternately, consolidation may be achieved by molding under heat andpressure in a suitable molding apparatus. Generally, molding isconducted at a pressure of from about 50 psi (344.7 kPa) to about 5,000psi (34,470 kPa), more preferably about 100 psi (689.5 kPa) to about3,000 psi (20,680 kPa), most preferably from about 150 psi (1,034 kPa)to about 1,500 psi (10,340 kPa). Molding may alternately be conducted athigher pressures of from about 5,000 psi (34,470 kPa) to about 15,000psi (103,410 kPa), more preferably from about 750 psi (5,171 kPa) toabout 5,000 psi, and more preferably from about 1,000 psi to about 5,000psi. The molding step may take from about 4 seconds to about 45 minutes.Preferred molding temperatures range from about 200° F. (˜93° C.) toabout 350° F. (˜177° C.), more preferably at a temperature from about200° F. to about 300° F. and most preferably at a temperature from about200° F. to about 280° F. The pressure under which the fiber layers andfabric composites of the invention are molded typically has a directeffect on the stiffness or flexibility of the resulting molded product.Molding at a higher pressure generally produces stiffer materials, up toa certain limit. In addition to the molding pressure, the quantity,thickness and composition of the fiber plies and polymeric bindercoating type also directly affects the stiffness of the articles formedfrom the composites.

While each of the molding and consolidation techniques described hereinare similar, each process is different. Particularly, molding is a batchprocess and consolidation is a generally continuous process. Further,molding typically involves the use of a mold, such as a shaped mold or amatch-die mold when forming a flat panel, and does not necessarilyresult in a planar product. Normally consolidation is done in a flat-bedlaminator, a calendar nip set or as a wet lamination to produce soft(flexible) body armor fabrics. Molding is typically reserved for themanufacture of hard armor, e.g. rigid plates. In either process,suitable temperatures, pressures and times are generally dependent onthe type of polymeric binder coating materials, polymeric bindercontent, process used and fiber type.

To produce a fabric article having sufficient ballistic resistanceproperties, the total weight of the binder/matrix coating preferablycomprises from about 2% to about 50% by weight, more preferably fromabout 5% to about 30%, more preferably from about 7% to about 20%, andmost preferably from about 11% to about 16% by weight of the fibers plusthe weight of the coating, wherein 16% is most preferred for non-wovenfabrics. A lower binder/matrix content is appropriate for woven fabrics,wherein a polymeric binder content of greater than zero but less than10% by weight of the fibers plus the weight of the coating is typicallymost preferred. This is not intended as limiting. For example,phenolic/PVB impregnated woven aramid fabrics are sometimes fabricatedwith a higher resin content of from about 20% to about 30%, althougharound 12% content is typically preferred.

Following weaving or consolidation of the fiber layers, an optionalthermoplastic polymer layer may be attached to one or both of the outersurfaces of the fibrous composite via conventional methods. Suitablepolymers for the thermoplastic polymer layer non-exclusively includethermoplastic polymers non-exclusively may be selected from the groupconsisting of polyolefins, polyamides, polyesters (particularlypolyethylene terephthalate (PET) and PET copolymers), polyurethanes,vinyl polymers, ethylene vinyl alcohol copolymers, ethylene octanecopolymers, acrylonitrile copolymers, acrylic polymers, vinyl polymers,polycarbonates, polystyrenes, fluoropolymers and the like, as well asco-polymers and mixtures thereof, including ethylene vinyl acetate (EVA)and ethylene acrylic acid. Also useful are natural and synthetic rubberpolymers. Of these, polyolefin and polyamide layers are preferred. Thepreferred polyolefin is a polyethylene. Non-limiting examples of usefulpolyethylenes are low density polyethylene (LDPE), linear low densitypolyethylene (LLDPE), Medium Density Polyethylene (MDPE), linear mediumdensity polyethylene (LMDPE), linear very-low density polyethylene(VLDPE), linear ultra-low density polyethylene (ULDPE), high densitypolyethylene (HDPE) and co-polymers and mixtures thereof. Also usefulare SPUNFAB® polyamide webs commercially available from Spunfab, Ltd, ofCuyahoga Falls, Ohio (trademark registered to Keuchel Associates, Inc.),as well as THERMOPLAST™ and HELIOPLAST™ webs, nets and films,commercially available from Protechnic S.A. of Cernay, France. Thethermoplastic polymer layer may be bonded to the composite surfacesusing well known techniques, such as thermal lamination. Typically,laminating is done by positioning the individual layers on one anotherunder conditions of sufficient heat and pressure to cause the layers tocombine into a unitary film. The individual layers are positioned on oneanother, and the combination is then typically passed through the nip ofa pair of heated laminating rollers by techniques well known in the art.Lamination heating may be conducted at temperatures ranging from about95° C. to about 175° C., preferably from about 105° C. to about 175° C.,at pressures ranging from about 5 psig (0.034 MPa) to about 100 psig(0.69 MPa), for from about 5 seconds to about 36 hours, preferably fromabout 30 seconds to about 24 hours.

The thickness of the individual fabrics/composites/fiber layers willcorrespond to the thickness of the individual fibers and the number offiber layers incorporated into a fabric. A preferred woven fabric willhave a preferred thickness of from about 25 μm to about 600 μm perlayer, more preferably from about 50 μm to about 385 μm and mostpreferably from about 75 μm to about 255 μm per layer. A preferrednon-woven fabric, i.e. a non-woven, single-layer, consolidated network,will have a preferred thickness of from about 12 μm to about 600 μm,more preferably from about 50 μm to about 385 μm and most preferablyfrom about 75 μm to about 255 μm, wherein a single-layer, consolidatednetwork typically includes two consolidated plies (i.e. two unitapes).Any thermoplastic polymer layers are preferably very thin, havingpreferred layer thicknesses of from about 1 μm to about 250 μm, morepreferably from about 5 μm to about 25 μm and most preferably from about5 μm to about 9 μm. Discontinuous webs such as SPUNFAB® non-woven websare preferably applied with a basis weight of 6 grams per square meter(gsm). While such thicknesses are preferred, it is to be understood thatother thicknesses may be produced to satisfy a particular need and yetfall within the scope of the present invention.

The fabrics/composites of the invention will have a preferred arealdensity prior to consolidation/molding of from about 20 grams/m² (0.004lb/ft² (psf)) to about 1000 gsm (0.2 psf). More preferable arealdensities for the fabrics/composites of this invention prior toconsolidation/molding will range from about 30 gsm (0.006 psf) to about500 gsm (0.1 psf). The most preferred areal density forfabrics/composites of this invention will range from about 50 gsm (0.01psf) to about 250 gsm (0.05 psf) prior to consolidation/molding.Articles of the invention comprising multiple fiber layers stacked oneupon another and consolidated will have a preferred composite arealdensity of from about 1000 gsm (˜0.2 psf) to about 40,000 gsm (8.2 psf),more preferably from about 2000 gsm (˜0.41 psf) to about 30,000 gsm (6.1psf), more preferably from about 3000 gsm (˜0.61 psf) to about 20,000gsm (4.1 psf), and most preferably from about 3750 gsm (0.77 psf) toabout 15,000 gsm (3.1 psf). A typical range for composite articlesshaped into helmets is from about 7,500 gsm (1.54 psf) to about 12,500gsm (2.56 psf).

The fabrics of the invention may be used in various applications to forma variety of different ballistic resistant articles using well knowntechniques, including flexible, soft armor articles as well as rigid,hard armor articles. For example, suitable techniques for formingballistic resistant articles are described in, for example, U.S. Pat.Nos. 4,623,574, 4,650,710, 4,748,064, 5,552,208, 5,587,230, 6,642,159,6,841,492 and 6,846,758, all of which are incorporated herein byreference to the extent not incompatible herewith. The composites areparticularly useful for the formation of hard armor and shaped orunshaped sub-assembly intermediates formed in the process of fabricatinghard armor articles. By “hard” armor is meant an article, such ashelmets, panels for military vehicles, or protective shields, which havesufficient mechanical strength so that it maintains structural rigiditywhen subjected to a significant amount of stress and is capable of beingfreestanding without collapsing. Such hard articles are preferably, butnot exclusively, formed using a high tensile modulus binder material.

The structures can be cut into a plurality of discrete sheets andstacked for formation into an article or they can be formed into aprecursor which is subsequently used to form an article. Such techniquesare well known in the art. In a most preferred embodiment of theinvention, a plurality of fiber layers are provided, each comprising aconsolidated plurality of fiber plies, wherein a thermoplastic polymeris bonded to at least one outer surface of each fiber layer eitherbefore, during or after a consolidation step which consolidates theplurality of fiber plies, wherein the plurality of fiber layers aresubsequently merged by another consolidation step which consolidates theplurality of fiber layers into an armor article or sub-assembly of anarmor article.

The ballistic resistance properties of the fibrous composites of theinvention, including both ballistic penetration resistance and backfacesignature, may be measured according to well known techniques in theart.

The following examples serve to illustrate the invention.

Examples 1-10

In Examples 1-10, the physical properties of ultra high molecular weightpolyethylene fibers were measured without being washed to remove theirfiber finish and without being plasma treated. The fiber samples for allof Examples 1-30 were selected from the same spool of ultra highmolecular weight polyethylene fibers.

The fiber denier, fiber load at maximum strain (pounds force, lbf),percent strain at maximum load, fiber tenacity (g/denier) and fiberinitial tensile modulus (g/denier) were measured for ten control fibersamples. The results are outlined in Table 1 wherein the fibers areidentified as Control fibers 1-10.

TABLE 1 Fiber Load at Strain at Fiber Initial Fiber Maximum MaximumTenacity Modulus Ex Sample ID Denier (lbf) (%) (g/denier) (g/denier) 1Control 1 1290 117.10 3.698 41.2 1288 2 Control 2 1290 113.30 3.567 39.81285 3 Control 3 1290 111.60 3.600 39.3 1265 4 Control 4 1290 116.703.667 41.0 1270 5 Control 5 1290 102.60 3.167 36.1 1280 6 Control 6 1290114.10 3.533 40.1 1295 7 Control 7 1290 106.80 3.433 37.5 1247 8 Control8 1290 111.80 3.433 39.3 1298 9 Control 9 1290 107.10 3.233 37.7 1286 10Control 10 1290 100.30 3.167 35.3 1245 AVERAGES 1290 106.4 3.28 37.41276

Examples 11-20

In Examples 11-20, the physical properties of ultra high molecularweight polyethylene fibers were measured after being washed tosubstantially remove their fiber finish but without being plasmatreated. The fiber samples for all of Examples 1-30 were selected fromthe same spool of ultra high molecular weight polyethylene fibers.

To remove the finish, the fibers were directed through a pre-soak waterbath containing de-ionized water, with an approximate residence time ofabout 18 seconds. After exiting the pre-soak water bath, the fibers wererinsed by a bank of 30 water nozzles. Water pressure of each waternozzle was approximately 42 psi with a water flow rate of approximately0.5 gallons per minute per nozzle. The water exiting the nozzles wasformed as a relatively flat stream and the angle of water contact on thefibers was either 0° or 30° relative to the angle of incidence of thestream emitting from adjacent nozzles. Water temperature was measured as28.9° C. The line speed through the bank of water nozzles wasapproximately 12 ft/min. The water in the soak bath and water deliveredto the nozzles was deionized by first passing through a separatede-ionizing system. The washed fibers were then dried and analyzed.

The fiber denier, fiber load at maximum strain, percent strain atmaximum load, fiber tenacity and fiber initial tensile modulus weremeasured for ten washed fiber samples. The results are outlined in Table2 wherein the fibers are identified as Washed fibers 1-10.

TABLE 2 Load at Strain at Fiber Fiber Initial Fiber Maximum MaximumTenacity Modulus Ex Sample ID Denier (lbf) (%) (g/denier) (g/denier) 11Washed 1 1290 110.70 3.366 38.9 1303 12 Washed 2 1290 109.90 3.366 38.61317 13 Washed 3 1290 101.20 2.934 35.6 1303 14 Washed 4 1290 101.103.033 35.6 1299 15 Washed 5 1290 100.50 3.000 35.3 1301 16 Washed 6 129099.69 2.934 35.1 1286 17 Washed 7 1290 99.46 2.967 35.0 1301 18 Washed 81290 92.46 2.800 32.5 1275 19 Washed 9 1290 98.12 2.967 34.5 1280 20Washed 10 1290 110.40 3.300 38.8 1289 AVERAGES 1290 100.3 3.02 35.3 1281

Examples 21-30

In Examples 21-30, the physical properties of ultra high molecularweight polyethylene fibers were measured after being washed tosubstantially remove their fiber finish and then also subsequentlyplasma treated. The fiber samples for all of Examples 1-30 were selectedfrom the same spool of ultra high molecular weight polyethylene fibers.

The fiber finish was substantially removed according to the processdescribed for Examples 11-20. Plasma treatment was conducted bycontinuously passing the washed fibers through an atmospheric plasmatreater (model: Enercon Plasma3 Station Model APT12DF-150/2, fromEnercon Industries Corp., having 29-inch wide electrodes) at a linespeed of approximately 12 ft/min, with a residence time of the fiberswithin the plasma treater of approximately 2.5 seconds and with theplasma treater set to a power of 1.5 kW. Treatment was conducted understandard atmospheric pressure (760 torr) in an atmosphere of 90% argongas and 10% oxygen.

The fiber denier, fiber load at maximum strain, percent strain atmaximum load, fiber tenacity and fiber initial tensile modulus weremeasured for ten washed fiber samples. The results are outlined in Table3 wherein the fibers are identified as W&P fibers (washed and plasmatreated fibers) 1-10.

TABLE 3 Fiber Load at Strain at Fiber Initial Fiber Maximum MaximumTenacity Modulus Ex Sample ID Denier (lbf) (%) (g/denier) (g/denier) 21W&P 1 1290 112.10 3.366 39.4 1293 22 W&P 2 1290 104.00 3.200 36.6 126823 W&P 3 1290 110.40 3.233 38.8 1291 24 W&P 4 1290 110.60 3.333 38.91325 25 W&P 5 1290 106.20 3.100 37.3 1309 26 W&P 6 1290 108.30 3.16738.1 1297 27 W&P 7 1290 111.70 3.366 39.3 1306 28 W&P 8 1290 100.902.934 35.5 1293 29 W&P 9 1290 107.70 3.133 37.9 1311 30 W&P 10 1290113.50 3.300 39.9 1328 AVERAGES 1290 107.4 3.12 37.8 1311Conclusions:

Collectively, Examples 1-30 illustrate that fibers that were plasmatreated after washing the fibers to substantially remove the fiberfinish have approximately the same physical properties both before andafter the treatments. Particularly, the combined treatments resulted inapproximately no loss in fiber tenacity and, in many instances, resultedin an increase in initial tensile modulus. Based on the fiber propertyaverages, the examples show a tenacity gain of approximately 1% and aninitial tensile modulus increase of approximately 2.7% when washing thefibers before plasma treating. The increases in tenacity and initialtensile modulus may result, for example, from crosslinking polymerchains at the fiber surfaces due to plasma treatment directly on thefiber surfaces rather than through a fiber surface finish.

Comparative Examples 1-6

In Comparative Examples 1-6, the physical properties of ultra highmolecular weight polyethylene fibers were measured after plasma treatingbut without being washed to remove their fiber finish before the plasmatreatment. The fiber samples for all of Comparative Examples 1-6 wereselected from the same spool of ultra high molecular weight polyethylenefibers.

The fiber denier, fiber load at maximum strain, percent strain atmaximum load, fiber tenacity and fiber initial tensile modulus weremeasured for three control fiber samples and three plasma treatedsamples. Plasma treatment was conducted by continuously passing thewashed fibers through a low pressure plasma treater (Plasma ScienceModel PS1010, commercially available from Plasmatreat US LP of Elgin,Ill.; modified to allow a single fiber to make multiple passes throughthe plasma atmosphere before exiting the chamber) at a line speed ofapproximately 10 m/min, with a residence time of the fibers within theplasma treater of approximately 1.4 minutes and with the plasma treaterset to a power of 250 W. Treatment was conducted at a pressure of 400milliTorr in an atmosphere of 90% argon gas and 10% oxygen. The resultsare outlined in Table 4 and Table 5.

TABLE 4 Plasma Line Plasma Plasma Example Sample ID Treated Speed GasPower Comp. 1 Control A No N/A N/A N/A Comp. 2 Control B No N/A N/A N/AComp. 3 Control C No N/A N/A N/A Comp. 4 Plasma A Yes 10 m/min 90%Argon; 250 W 10% Oxygen Comp. 5 Plasma B Yes 10 m/min 90% Argon; 250 W10% Oxygen Comp. 6 Plasma C Yes 10 m/min 90% Argon; 250 W 10% Oxygen

TABLE 5 Load at Strain at Fiber Maxi- Maxi- Fiber Initial Sample Fibermum mum Tenacity Modulus Ex ID Denier (lbf) (%) (g/denier) (g/denier)Comp. 1 Control 1268 108.60 3.227 38.9 1269 A Comp. 2 Control 1253108.50 3.250 39.3 1281 B Comp. 3 Control 1250 106.30 3.133 38.6 1284 CAVGERAGE 1257 107.8 3.20 38.9 1278 Comp. 4 Plasma 1274 90.44 2.563 32.21313 A Comp. 5 Plasma 1262 89.41 2.567 32.1 1316 B Comp. 6 Plasma 127488.78 2.470 31.6 1303 C AVERAGE 1270 89.5 2.53 32.0 1311Conclusions:

Collectively, Comparative Examples 1-6 illustrate that fibers that wereplasma treated without first washing the fibers to substantially removethe fiber finish experience a significant loss in fiber tenacity due tothe plasma treatment, a tenacity loss of approximately 17% based on thefiber averages. This is particularly revealing in view of thesubstantially less aggressive plasma treatment level in ComparativeExamples 1-6 (i.e. 250 W) at low pressure relative to the plasmatreatment level in Examples 1-30 (i.e. 1.5 kW) at atmospheric pressure.

Example 31

A four-ply non-woven composite was fabricated incorporating four pliesof unidirectionally oriented, substantially parallel ultra highmolecular weight polyethylene fibers having a fiber tenacity ofapproximately 45 g/d.

Prior to forming the plies, the fibers were washed to substantiallyremove their fiber finish and subsequently plasma treated and dried. Toremove the finish, a plurality of multi-filament fibers were unwoundfrom a plurality of fiber spools (one spool per multi-filament fiber)and then passed through a fixed collimating comb to organize the fibersinto an evenly spaced fiber web. The fiber web was then directed througha pre-soak water bath containing de-ionized water, with an approximateresidence time of about 18 seconds. After exiting the pre-soak waterbath, the fibers were rinsed by a bank of 30 water nozzles. Waterpressure of each water nozzle was approximately 42 psi with a water flowrate of approximately 0.5 gallons per minute per nozzle. The waterexiting the nozzles was formed as a relatively flat stream and the angleof water contact on the fibers was either 0° or 30° relative to theangle of incidence of the stream emitting from adjacent nozzles. Watertemperature was measured as 28.9° C. Line speeds through the pre-soakwater bath and through the bank of water nozzles ranged from about 4m/min to about 20 m/min. The water in the soak bath and water deliveredto the nozzles was deionized by first passing through a separatede-ionizing system. The washed fibers were then dried and transferredfor further processing.

Plasma treatment was conducted by continuously passing a 29-inch wideweb of washed fibers through an atmospheric plasma treater (model:Enercon Plasma3 Station Model APT12DF-150/2, from Enercon IndustriesCorp., having 29-inch wide electrodes) at a rate of approximately 12ft/min, with the plasma treater set to a power of 1.5 kW. This resultedin a power distribution over the area of the fibers, measured in wattdensity, of 2000 W/(29 in.×12-FPM) or 67 Watts/ft²/min applied to thefibers. The residence time of the fibers within the plasma treater wasapproximately 2.5 seconds. Treatment was conducted under standardatmospheric pressure. The fiber tenacity after the plasma treatment wasapproximately 45 g/d.

Thereafter, the fibers were coated with an aliphatic, anionicpolyurethane dispersion having a modulus of 1100 psi. Each ply had aresin content of approximately 16% by weight of the ply. The four plieswere oriented at 0°/90°/0°/90° relative to the longitudinal fiberdirection of each ply. The four-ply composite had a fiber areal density(per ply) of approximately 35 gsm and a total areal density of each plyof approximately 42 gsm, which translates to a final product FAD and TADof 140 gsm and 167 gsm, respectively.

Example 32

The composite of Example 31 was fabricated into a consolidated 2.0 psfsample and tested for backface signature and V₅₀ at room temperature.The average V₅₀ value against a 16-Grain RCC projectile at ambient roomtemperature was 3621 feet/second. The average BFS at ambient roomtemperature against the same 16-Grain RCC projectile was 3 mm asmeasured with a ½ inch air gap between the rear surface of the compositeand the clay backing material.

Backface Signature Measurement

Backface signature was measured using an apparatus described in patentapplication Ser. No. 61/531,233. The composite was spaced apart from aclay block by ½ inch (12.7 mm) by inserting a custom machined spacerelement between the composite article and the clay block. The custommachined spacer element comprised an element having a border and aninterior cavity defined by said border wherein the clay was exposedthrough the cavity, and wherein the spacer was positioned in directcontact with front surface of the clay. Projectiles were fired at thecomposite articles at target locations corresponding to the interiorcavity of the spacer. The projectiles impacted the composite article atlocations corresponding to the interior cavity of the spacer, and eachprojectile impact caused a measurable depression in the clay. The 3 mmBFS measurement refers to the depth of the depression in the clay as perthis method without taking into account the depth of the spacer element,i.e. the BFS measurement does not include the actual distance betweenthe composite and the clay.

V₅₀ Measurement

V₅₀ data was acquired taken under conventionally known standardizedtechniques, particularly per the conditions of Department of DefenseTest Method Standard MIL-STD-662F against a 16-Grain RCC projectile.

Examples 33-38

Examples 31 and 32 were repeated to fabricate additional 2.0 psf samplesbut with different binder resins. The composites were tested forbackface signature and V₅₀ at room temperature, and the results areoutlined in Table 6. For examples 36-38, corona treatment was conductedrather than a plasma treatment as in Example 31. Corona treatment wasperformed by continuously passing a web of washed fibers through acorona treater having 30-inch wide electrodes at a rate of approximately15 ft/min, with the corona treater set to a power of 2 kW. The residencetime of the fibers within the corona field was approximately 2 seconds.Treatment was conducted under standard atmospheric pressure.

TABLE 6 RESIN MODULUS @ EXAM- TREAT- 100% Elongation AVG AVG PLE MENTRESIN (psi) V₅₀ BFS 32 Wash & Aliphatic 1100 3621 3.0 Plasma Polyether-Based Polyurethane 33 Wash & Aqueous 725 3533 6.75 Plasma PolyurethaneDispersion 34 Wash & Aqueous 2900 3487 2.25 Plasma PolyurethaneDispersion 35 Wash & Aliphatic 1100 3459 3.5 Plasma Polyether- BasedPolyurethane 36 Wash & Aqueous 2900 3287 3.75 Corona PolyurethaneDispersion 37 Wash & Aqueous 725 3349 5.25 Corona PolyurethaneDispersion 38 Wash & Aliphatic 1100 3223 2.625 Corona Polyether- BasedPolyurethane

Example 39

A plurality of composites of Example 31 are cut into a plurality of21″×21″ squares. A plurality of the squares are fabricated into one ormore ballistic shells, and the ballistic shells are fabricated intoEnhanced Combat Helmets. Each ballistic shell weighs approximately 2.8lbs (˜2.24 psf). There is a polymer based outer surface coating or thickfilm on the outside of the helmet, and a woven polyethylene based fabricon the inside of the helmet (e.g. woven fabric style 903 incorporating1200 denier, S900 SPECTRA® polyethylene fibers; plain weave with a pickcount of 21×21 ends/inch (ends/2.54 cm); areal weight of 7 oz/yd² (217g/m2 (gsm)). The helmets are optionally finished with pads andsuspensions.

Example 40

A four-ply non-woven composite was fabricated incorporating four pliesof unidirectionally oriented, substantially parallel 45 g/d fibers. Thefibers were washed to substantially remove their fiber finish andsubsequently plasma treated and dried. The fiber tenacity after theplasma treatment was 45 g/d. Thereafter, the fibers were coated with analiphatic, anionic polyurethane dispersion having a modulus of 1100 psi.Each ply had a resin content of approximately 16% by weight of the ply.The four plies were oriented at 0°/90°/0°/90° relative to thelongitudinal fiber direction of each ply. The four-ply composite had afiber areal density (per ply) of approximately 53 gsm and a total arealdensity of each ply of approximately 64 gsm.

While the present invention has been particularly shown and describedwith reference to preferred embodiments, it will be readily appreciatedby those of ordinary skill in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe invention. It is intended that the claims be interpreted to coverthe disclosed embodiment, those alternatives which have been discussedabove and all equivalents thereto.

What is claimed is:
 1. A modified, high tenacity fiber having fiber surfaces that are partially covered by a fiber surface finish, wherein from 50% to 99.0% of the fiber surface area is exposed and not covered by the fiber surface finish, which fiber has been modified by a plasma treatment at a plasma energy flux of about 100 W/ft²/min or less, or modified by a corona treatment with an energy of from about 2 Watts/ft²/min to about 100 Watts/ft²/min.
 2. A multi-fiber yarn comprising a plurality of modified, high tenacity fibers of claim 1, wherein said modified, high tenacity fibers comprise ultra-high molecular weight polyethylene fibers.
 3. A fiber ply comprising a plurality of modified, high tenacity fibers of claim 1, which plurality of fibers are aligned in a substantially parallel array.
 4. A fabric formed from a plurality of modified, high tenacity fibers of claim
 1. 5. A fibrous composite comprising a plurality of modified, high tenacity fibers of claim 1 and a polymeric binder material at least partially coated on at least some of said modified fibers.
 6. The fibrous composite of claim 5 which comprises a consolidated plurality of fiber plies, each fiber ply comprising a plurality of modified, high tenacity fibers of claim 1 and wherein a polymeric binder material is at least partially coated on at least some of said modified fibers.
 7. The fibrous composite of claim 6 wherein said composite has a V₅₀ value of at least about 3300 feet/sec against a 16-grain Right Circular Cylinder projectile in accordance with Department of Defense Test Method Standard MIL-STD-662F and a backface signature of about 5 mm or less when impacted with a 124-grain, 9 mm FMJ RN projectile fired at a velocity of from about 427 m/s to about 445 m/s (1430 feet/second (fps)±30 fps), each being measured for a composite having an areal density of approximately 2.0 lbs/ft².
 8. The fibrous composite of claim 7 wherein said polymeric binder material comprises an aliphatic polyurethane.
 9. An article formed from the fibrous composite of claim
 7. 10. The modified, high tenacity fiber of claim 1 wherein the residual finish is present on the fiber surfaces as patches of residual finish and wherein from 90% to 99.0% of the fiber surface area is exposed and not covered by the residual finish.
 11. The modified, high tenacity fiber of claim 1 wherein the fiber is produced by treating the fibers in a chamber maintained at about atmospheric pressure or above atmospheric pressure, and wherein said modified, high tenacity fiber has a tenacity of at least about 50 g/denier at ambient room temperature.
 12. The modified, high tenacity fiber of claim 1 wherein said modified fiber has a tenacity of at least about 60 g/denier at ambient room temperature.
 13. The modified, high tenacity fiber of claim 1 wherein said modified fiber has a tenacity of at least about 55 g/denier at ambient room temperature.
 14. A modified, high tenacity fiber which has been modified by a plasma treatment or modified by a corona treatment, said modified, high tenacity fiber having a tenacity of at least about 33 g/denier at ambient room temperature, said fiber being produced by a process comprising the steps of: a) providing a high tenacity fiber having a tenacity of at least about 33 g/denier at ambient room temperature, wherein said fiber has fiber surfaces and wherein said surfaces are at least partially covered by a fiber surface finish; b) washing the fibers to remove only a portion of the fiber surface finish from the fiber surfaces wherein a residual finish remains on the fiber surfaces; and c) subjecting the high tenacity fiber to a plasma treatment or to a corona treatment under conditions effective to modify the high tenacity fiber; wherein the high tenacity fiber is plasma treated with a plasma energy flux of about 100 W/ft²/min or less, or wherein the high tenacity fiber is corona treated with an energy of from about 2 Watts/ft²/min to about 100 Watts/ft²/min; thereby producing a modified, high tenacity fiber which has been modified by a plasma treatment or modified by a corona treatment, which modified high tenacity fiber has a tenacity of at least about 33 g/denier at ambient room temperature, and wherein from 50% to 99.0% of the fiber surface area is exposed and not covered by the residual fiber surface finish.
 15. The modified, high tenacity fiber of claim 14 wherein the fibers are washed with water, and wherein said modified, high tenacity fiber comprises ultra-high molecular weight polyethylene.
 16. The modified, high tenacity fiber of claim 14 wherein said modified fiber has a tenacity of at least about 50 g/denier at ambient room temperature.
 17. The modified, high tenacity fiber of claim 14 wherein the residual finish is present on the fiber surfaces as patches of residual finish and wherein from 75% to 99.0% of the fiber surface area is exposed and not covered by the residual finish.
 18. The modified, high tenacity fiber of claim 14 wherein said residual finish is present in an amount of less than or equal to about 0.5% by weight based on the weight of the fiber plus the weight of the finish.
 19. The modified, high tenacity fiber of claim 14 wherein step c) is conducted in a chamber maintained at about atmospheric pressure or above atmospheric pressure.
 20. A modified, high tenacity fiber having fiber surfaces that are substantially free of a fiber surface finish, which fiber has been modified by a plasma treatment at a plasma energy flux of about 100 W/ft²/min or less, or modified by a corona treatment with an energy of from about 2 Watts/ft²/min to about 100 Watts/ft²/min, said modified, high tenacity fiber having a tenacity of at least about 45 g/denier at ambient room temperature, wherein from 95% to 99.0% of the fiber surface area is exposed and not covered by a fiber surface finish. 